1. Field of the Invention
The present invention relates to a semiconductor device and its manufacturing method, and more particularly, it relates to a semiconductor device which uses silicon germanium and its manufacturing method.
2. Description of the Related Art
Miniaturization of a semiconductor device has been accompanied by attention paid to a strained silicon device to achieve a higher speed operation in a metal oxide semiconductor (MOS) device. In a complementally MOS field effect transistor (CMOSFET) formed on silicon, since carrier (i.e., hole) mobility in a channel region of p channel MOSFET (pMOS) is lower than carrier (i.e., electron) mobility in a channel region of an n channel MOSFET (nMOS), pMOS operating in a higher speed is desired to be achieved. In the pMOS, it is known that the carrier (i.e., hole) mobility is enhanced by applying compressive stress to the channel region.
There is known a method of enhancing carrier (i.e., hole) mobility by applying compressive stress to the channel region by using a semiconductor having larger atomic radius than that of silicon, such as germanium or silicon germanium (SiGe), for a source/drain and/or source/drain extension of a silicon pMOS device (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 8-186257).
Additionally, a method of efficiently forming an SiGe layer on a drain extension and/or a drain is disclosed by P. R. Childambaram et al., in 2004 Symposium on VLSI Technology Digest of Technical Papers, pp. 48-49. According to this method, a shallow trench is formed in a silicon substrate on which a SiGe layer is selectively formed by epitaxial growth, then the drain extension and/or the drain are formed therein. Further, a silicide layer (e.g., nickel silicide layer (NiSi)) is formed on the drain of the SiGe layer.
However, if germanium is contained in the source/drain on which the silicide layer is formed, a problem of a deposition failure such as agglomeration of silicide metal (e.g., nickel) and/or peeling off of the silicide film or the like occurs during the formation of the silicide layer on the source/drain.
To solve the problem, an attempt has been made to prevent the deposition failure by epitaxially growing a silicon film on the source/drain made of SiGe, and then forming the silicide layer thereon. However, if a portion of the silicon film is not sufficiently thick, there is a possibility to cause segregation of a silicide metal (e.g., Ni) due to contacting the silicide layer with the SiGe layer.